Properties of a diamond, which is a carbon crystal, not only include extreme hardness and superior abrasion resistance but also include superior slidability and thermal conductivity as well as a high refractive index. Due to having such properties, for example, diamonds are used as cutting tools such as a bite, an end mill, and a file, plastic working dies such as a punch and a die, sliding members such as a valve lifter and a bearing, heat dissipating members such as a heat sink, electronic substrates, and optical parts such as a lens and a window. Such diamond products are machined in accordance with their applications and are generally required to have a polished smooth surface. Applications of polished diamonds include press dies such as a die and a punch, sliding portions in a bearing, automotive parts and the like, cutting tools such as a bite and an end mill, a heat sink or an electronic substrate of electronic devices, and optical parts.
While mechanical polishing methods which also use a diamond as polishing means in the form of abrasive grains or a whetstone were adopted for polishing a diamond surface in the past, since polishing using these methods are not only time-consuming but also cause simultaneous cutting, there were problems of a short tool life and an inadequacy with respect to polishing a diamond surface that is a three-dimensional surface with irregularities instead of a flat surface.
While a polishing method disclosed in Patent Literature 1 adopts a preheating method by laser irradiation and performs polishing by causing a chemical reaction between a metal constituting a polishing member and carbon on a diamond surface, an object of this invention is to provide a diamond surface polishing method which ensures that a polishing member has a long service life, which enables the polishing member to be readily controlled, which produces a surface with high smoothness, and which is readily applicable even to polishing three-dimensional surfaces with irregularities and to provide a diamond surface polishing method which enables polishing to be performed using a polishing member formed by an inexpensive simple metal instead of using an expensive material obtained by a special production method such as an intermetallic compound. To this end, as shown in FIG. 10, this invention provides a diamond surface polishing method in which a polishing member 3 or a diamond surface 1a is heated by a laser beam 2a or the like prior to polishing by the polishing member, which has a linear or belt-like shape and at least a surface of which is made of a metal easily reactive with carbon or a carburizing metal is used as the polishing member 3. Polishing is performed by moving a polished object 1 by applying pressure to a diamond surface via a polishing member supporting tool 4, which is a pulley, a roller, or the like, while winding the polishing member 3 around the polishing member supporting tool 4 and continuously or intermittently paying out the polishing member.
In addition, Patent Literature 2 is a description of an invention titled “Diamond surface polishing method” previously filed as a patent application by the present applicants, the contents of which relate to a method for polishing a diamond while removing abrasive powder remaining on a surface of the diamond. Patent Literature 2 describes that this invention is a diamond surface polishing method which uses a metallic polishing member and heats the polishing member and/or a diamond surface and which polishes while removing, by rubbing, abrasive powder derived from the polishing member remaining on the diamond surface, and that preferred specific examples include: (1) when removing the abrasive powder, using at least one means selected from a group consisting of a finishing tool, a dressing tool, a shot blast, fluidic injection, electrostatic force, magnetic force, and adhesive force; and (2) when removing the abrasive powder, further using air blowing or vacuuming. According to this diamond surface polishing method, by rubbing a diamond surface being polished with a finishing tool or the like, metal powder (abrasive powder) derived from the polishing member adhering to irregularities of the diamond surface can be effectively removed and a problem of adhesion created by subjecting the abrasive powder to heat and pressure can be solved.
When polishing a diamond surface using a conventional polishing method, even if polishing is performed in a state where a polishing member is brought into contact with a surface of a polished object at a constant pressing force, there is a problem in that non-uniform polishing occurs when the contour shape of the polished object is non-uniform, such as a shape with irregularities, instead of a uniform flat shape.